Reciprocable hydro-pneumatic motor



tates This invention relates to fluid pressure motors and, in particular, to reciprocable fluid pressure motors.

Hitherto, mechanical coil spring workpiece holddown devices have been used in sheet metal forming presses for holding down the sheet metal blanks or workpieces while the punch and die are forming the blank into a threedimensional workpiece and also for continuing to hold down the workpiece while it is being stripped or separated from the punch during the retraction stroke of the press platen or ram. Such coil spring workpiece holddown devices have the disadvantage of not applying their full holddown pressures until after the stroke of the press has been partway performed. The present invention provides a reciprocable hydro-pneumatic motor which eliminates these inadequacies of prior mechanical coil spring workpiece holddown devices.

In particular, one object of this invention is to provide a reciprocable hydro-pneumatic motor which applies a maximum workpiece holddown force immediately at the beginning of the forward or working stroke of the press, yields in a predetermined manner as the forming of the workpiece progresses, and which continues to provide a holddown force during the retraction stroke of the ram or platen so as to hold the formed workpiece in position during the stripping of the punch from the workpiece.

Another object is to provide a reciprocable hydropneumatic motor of the foregoing character having a main hydraulic piston which engages a substantially incompressible hydraulic fluid such as oil, and an auxiliary pneumatic piston which engages a compressible pneumatic fluid, such as a gas, in response to the force of hydraulic fluid against it produced by the stroke of the hydraulic piston in one direction of its reciprocation.

Another object is to provide a reciprocable hydropneumatic motor of the foregoing character wherein the main hydraulic piston reciprocates in a hydraulic cylinder containing hydraulic fluid and the auxiliary pneumatic piston reciprocates within the hollow piston rod of the main hydraulic piston, the hollow piston rod containing hydraulic and pneumatic fluids on opposite sides of the auxiliary pneumatic piston.

Another object is to provide a reciprocable hydropneumatic motor of the foregoing character wherein the main hydraulic piston is provided with a check valve which gives a more rapid action during the retraction stroke aided by the compressed gas behind the auxiliary pneumatic piston which has been compressed by the force of the hydraulic fluid against it during the forward stroke.

Another object is to provide a reciprocable hydropneumatic motor of the foregoing character wherein the auxiliary pneumatic piston is a free piston capable of free reciprocation within the hollow piston rod of the main hydraulic piston.

Another object is to provide a reciprocable hydro-pneumatic motor of the foregoing character which can be installed in any desired position, either vertical or horizontal as may be most suitable for the particular instal lation, and with the cylinder above or below the main hydraulic piston, the hollow piston rod of which contains the auxiliary pneumatic piston.

Another object is to provide a reciprocable hydropneumatic motor of the foregoing character which dissipates its own heat during operation, and does not transmit such heat to other such motors, hence divides the 'fatent production and dissipation of heat among the several individual motors.

Another object is to provide a reciprocable hydropneumatic motor of the foregoing character wherein means is provided for amplifying the pneumatic pressure of the gas behind the auxiliary pneumatic piston, such as by an accumulator.

Other objects and advantages of the invention will become apparent during the course of the following description of the accompanying drawings, wherein:

FIGURE 1 is a longitudinal section through a reciprocable hydro-pneumatic motor, according to one form of the invention, with the motor parts contracted;

FIGURE 2 is a view similar to FIGURE 1, with the motor parts extended;

FIGURE 3 is a cross-section through the main hydraulic piston head taken along the lines 33 in FIG- URE 1 and showing the outer valve ports therein;

FIGURE 4 is a diagrammatic vertical section through a conventional sheet metal forming press equipped with mating trimming or flanging dies in their closed position, showing in the upper portion thereof two reciprocable hydro-pneumatic motors of the present invention with their hydraulic cylinders mounted in the upper die or punch and connected to the work-holding pad so as to hold down the workpiece before and during trimming or flanging, as well as to continue to hold down the workpiece during stripping as the press platen returns to its open position during its retraction stroke;

FIGURE 5 is a diagrammatic vertical section through a conventional sheet metal forming press equipped with mating forming dies in their closed position, showing on the left-hand side thereof a reciprocable hydro-pneumatic motor of the present invention with the hydraulic cylinder mounted in the press bolster and showing on the right-hand side thereof a similar reciprocable hydro pneumatic motor with the hydraulic cylinder mounted in the lower die shoe; and

FIGURE 6 is a fragmentary longitudinal section through a modified hydro-pneumatic motor including pressure responsive flow control in the hydraulic piston head thereof.

Referring to the drawings in detail, FIGURE 1 shows a reciprocable hydro-pneumatic motor, generally desig nated 10, according to one form of the invention having a hydraulic cylinder 12 containing a cylinder bore 14. The latter is closed at one end by an end wall 16 and internally threaded at its open end 18 to receive a retaining ring 20 grooved to permit air to move inward and outward, thereby providing a cooling action. Reciprocably mounted in the cylinder bore 14 of the hydraulic cylinder 12 is the piston head 22 of a hydraulic piston, generally designated 24, having an elongated hollow piston rod 26 containing a longitudinal bore 28 coaxial with the cylinder bore 14 and closed at the end opposite the hydraulic piston head 22 by an end wall 30. The latter contains a threaded port 32 adapted to receive a coupling 34 for the connection of a pipe 36 leading to an accumulator (not shown). Alternatively where amplification of pneumatic pressure is not needed, the threaded port 32 is closed by a threaded plug in place of the coupling 34.

It will be understood that the terms hydraulic and pneumatic are used herein in the broad senses in which they are employed in the mechanical arts, namely to indicate relatively incompressible and compressible fluids respectively, rather than specifically water or air. As a matter of practice, oil is preferably used as the hydraulic fluid, and nitrogen as the pneumatic fluid, the latter for the purpose of preventing dieselling or internal combustion from the use of air containing oxygen, as a result of the high compression of the gas with consequent high production of heat.

Reciprocably mounted within the bore 28 of the hollow piston rod 26 is an auxiliary pneumatic piston, generally designated 38. The auxiliary pneumatic piston 38 is a free piston which divides the piston rod bore 28 into hydraulic intermediate and pneumatic end chambers 40 and 42 respectively to the left and to the right of the piston 38, these chambers 40 and 42 varying in length during operation, as is seen from a comparison of FIGURES 1 and 2. Hydraulic fiuid passes into and out of the chamber 40 from a hydraulic end chamber 44 at the left hand end of the hydraulic cylinder 12 through the hydraulic piston head 22 in a manner described below.

The hydraulic piston 24 includes a hollow enlargement 46 at its left hand or inner end forming the outer part of the hydraulic piston head 22, the enlargement 46 joining the hollow piston rod 26 in an annular shoulder 48. The enlargement 46 contains an annular tapered or conical valve seat 50 extending from the bore 28 to a counterbore 52, which in turn opens into an enlarged internallythreaded bore 54 at an annular shoulder 56. Threaded into the threaded enlarged bore 54 is an externallythreaded backing disc 58 having a plurality of parallel passageways 60 (FIGURES 1 and 3) communicating at their right hand ends with the counterbore 52 and at their left hand ends with aligned ports 62 in the end wall of a packing cup 64 of leather or other suitable material. The side walls of the packing cup 64 snugly engage the cylinder bore 14 so as to prevent leakage and are forced against it by the radial pressure of the hydraulic fluid within the chamber 44.

The backing disc 58 is provided with a central threaded bore 66 into which is threaded the externally-threaded shank 68 of a packing cup retaining screw 70 having a head 71, the periphery of which is provided with circumferentially-spaced grooves 72 aligned with the packing cup ports 62 and backing disc passageways 60. The retaining screw 70 has a central passageway 74 aligned with a small diameter passageway 76 in an annular externallythreaded plug 78 of tool steel or other suitable wear-resisting and heat-resisting material threaded into a threaded hole 89 in a valve disc 82. The valve disc 82 is reciprocably mounted in the counterbore S2 and has oppositely-tapered rim portions 84 and 85. The forward tapered rim portion 84 is adapted to snugly engage the tapered valve seat 58' in a liquid-flow-preventing engagement. The valve disc 82 is also of slightly less diameter than the counter-bore 52 so that it and the rearward tapered rim portion 85 permit fluid flow around the edge of the disc 82 and through the ports 60, as shown in FIG- URE l. The enlargement 46 of the hydraulic piston head 22 is annularly grooved as at 86 to receive a conventional O-ring 88 having sealing engagement with the cylinder bore 14.

The auxiliary pneumatic piston 38 (FIGURE 1) consists of a central head 90 which is annularly grooved as at 92 to receive a conventional Ci -ring 94 and which is centrally bored and threaded as at 96 to receive the externally-threaded stems 98 of packing retaining screws 1%, the heads 102 of which engage and clamp the end walls of packing cups 104 against the opposite sides of the head 90. The packing cups 184 are of leather or other suitable material and their rims or side Walls face in opposite directions and provide snug sealing engagement with the bore 28.

A typical installation of the reciprocable hydro-pneumatic motor in a trimming or flanging die set 108 mounted in a conventional sheet metal forming press, generally designated 110, is shown in FIGURE 4. The press 110 is equipped with the usual side frames 112 and a bed 1 14 upon which is mounted a bolster 116. A platen or ram 118 is reciprocated vertically by either conventional mechanical or hydraulic means (not shown). A recessed lower die shoe 120 is mounted on the bolster 116 and in turn supports the lower trimming or fianging die 122 which mates with an upper pad 124 of corresponding configuration. A recessed upper die shoe 126 is bolted or otherwise secured to the platen 118 and is bored to receive a pair of the cylinders 12 of the reciprocable hydro-pneumatic motors 10 of the present invention, the piston rods 26 of which extend downward and are secured to the upper pad 124. Mounted adjacent the upper pad 124 is a punch 128 secured to the upper die shoe 126 and movable relatively to the lower die 122 during the descent of the platen 118 to flange or cut otI the edge of a sheet metal workpiece W held between the lower die 122 and upper pad 124 while it is being thus worked upon. The upper pad 124 also holds down the workpiece W against the lower die 122 and, aided by the reciprocable hydro-pneumatic motors 18, assists in the stripping action of the punch 128 relatively to the workpiece W.

Another installation of the reciprocable hydro-pneumatic motor 10 in a drawing die set 130 mounted in the same conventional sheet metal forming press is shown in FIGURE 5. As before, a recessed lower die shoe 132 is mounted upon the bolster 116 and supports the lower die 134 which is configured to the desired shape for the workpiece W. Mating with the lower die 134 is a correspondingly-configured upper die or punch 136 bolted or otherwise secured to the press platen or ram 118 for vertical reciprocation therewith. Mounted beside and around the lower die 134 is a yieldinglymounted workpiece supporting lower pad 138. The pad 138 is bored on its underside to receive the ends of the piston rods 26 of the pistons 24 of the hydro-pneumatic motors 18 so as to yield at a controlled rate and pressure relatively to the cylinders 12 thereof. FIGURE 5 shows how, for convenience, the hydraulic cylinders 12 may be mounted in two different ways. On the left-hand side of FIGURE 5, the bolster 116 is recessed to receive the cylinder 12 and the lower die shoe 132 is bored for the passage of the piston rod 26, the upper end of which is seated in the lower side of the yielding lower pad 138. On the right hand side of FIGURE 5, the lower die shoe 132 is recessed to receive the hydraulic cylinder 12 and the piston rod 26 of the piston 24 is seated directly in the bottom of the lower pad 138.

In the operation of the reciprocable hydro-pneumatic motor 16, let it be assumed, for example, that the hydropneumatic motors 10 are mounted in the manner shown and described in connection with FIGURE 5 with their cylinders 12 at the bottom and held in a stationary position while their pistons 24 move upward and downward as regulated by the motion of the press platen upon the part to which the piston rods 26 of the pistons 24 are connected. Let is also be assumed that the parts are in the positions shown in FIGURE 2, with the pistons 24 at the uppermost limits of their strokes, ready to be forced downward by the press platen, such as the platen 118 of the press 110 of FIGURE 5. While the parts are in this condition and relative positions, the lower chambers 44 and the intermediate chambers 40 are filled with hydraulic fluid, such as oil, whereas the upper chambers 42 are filled with a compressible gas, such as nitrogen, with or without the assistance of additional compressed nitrogen supplied through the pipes 36 and couplings 34 from a conventional accumulator (not shown).

As the press platen 118 descends upon its forward or working stroke, carrying with it the upper die or punch 136 and the workpiece lower pads 138 (FIGURE 5), each of the hollow piston rods 26 of the pistons 24 is forced downward from the position of FIGURE 2 to that of FIGURE 1. The downward motion of each hydraulic piston head 22 against the hydraulic fluid in the chamber 44 forces the hydraulic fluid to flow through the central and peripheral passageways 74, 76, 72, 62, 69, thereby moving the check valve disc 82 away from the backing disc 58 and against the annular valve seat 50. Continued descent of the hydraulic piston 24 causes the hydraulic fluid to spurt through the check valve disc passageway 76 into the intermediate chamber 40 with a retarding action due to the restricted diameter of the passageway 76.

The continued descent of each hydraulic piston 24 (FIGURE 2) and the consequent collection of hydraulic pressure fluid in each intermediate chamber 40 forces each auxiliary piston 38 to move toward the piston rod end wall 30, further compressing the nitrogen or other pneumatic fluid within each end chamber 42. When each hydraulic piston 24 reaches the end of its compression stroke (FIGURE 1), its auxiliary piston 38 has been forced by the pressure of the hydraulic fluid in its intermediate chamber 40 to compress the gas in its end chamber 42 its maximum amount, thereby creating a standing pressure in each end chamber 42.

If, now, the motion of the press 110 is reversed, and the platen or ram 118 thereof moves upward on its retraction or return stroke, the hydraulic fluid in each chamber 40 forces each valve disc 82 off its seat 50 and against its respective retaining disc 58. At the same time, the standing pressure of the compressed gas within each end chamber 42 of each hollow piston rod 26 of each piston 24 acts against each auxiliary piston 38 to apply pressure to the entrapped hydraulic fluid in each intermediate chamber 40 of each bore 38. When this occurs, hydraulic fluid escapes from each chamber 40 both through the restricted orifice or passageway 76 and around the double-bevelled nm 89 of its respective valve disc 82 and thence through the outer passageways 60 into the hydraulic cylinder chamber 44. This brings about a rapid return of the hydraulic fluid from the chamber 40 to the chamber 44, with a consequently rapid retraction of the hydraulic piston 24 on its return or upward stroke.

As the press platen 118 continues to rise, the consequent rise of each hydraulic piston 24 causes its respective hydraulic piston head 22 and free auxiliary pneumatic piston 38 to approach one another (FIGURE 2) until the end of the retraction stroke is reached. Meanwhile, as stripping of the workpiece W occurs, the lower pad 138 effects a follow-up action upon the workpiece W to strip it from the lower die 134 as a result of the abovedescribed operation of the reciprocable hydro-pneumatic motors 10.

The operation of the reciprocable hydro-pneumatic motor in the installation shown in FIGURE 4, in association with the trimming or flanging die set 108, is believed to be sufficiently clear from the above description of the construction and operation, taken with the above description of the operation of the motor 10, itself. Accordingly, a repetition of such further description of operation is believed to be unnecessary.

The modified reciprocable hydro-pneumatic motor, generally designated 150, the modified portion of which 1s shown in FIGURE 6, is generally similar in construction to the reciprocable hydro-pneumatic motor shown in FIGURES l, 2 and 3, and corresponding parts are consequently designated with the same reference numerals. In the motor 150, the valve disc 82 of the piston head 24 is replaced in the piston head 151 of the hydraulic plunger 153 by a compound valve unit 152 which not only performs the functions performed by the valve disc 82 but also provides a pressure-responsive control over hydraulic fluid flow through the central piston head passageway 74.

For this purpose, the valve unit 152 includes a reciprocable valve member 154 having a disc-shaped oppositely-tapered head 156 and a hollow stem 158 projecting axially therefrom. The head 156 is provided with a central fluid passageway 160 terminating in a tapered valve seat 162 which in turn opens into an axial bore 164. The latter terminates in an internally-threaded counterbore 166 containing a threaded plug 168 with a vent 170 of restricted diameter therein. Reciprocably mounted in the bore 164 is a hollow approximately cylindrical auxiliary valve member 172 with a tapered nose portion 174 urged into engagement with the tapered valve seat 162 by a helical compression spring 176, the rearward end of which engages the plug 168 as a spring abutment. The stem 158 adjacent its junction with the head 156 is provided with a number of approximately transverse fluid passageways 178 opening into the bore 164 adjacent the tapered valve seat 162.

The modified reciprocable hydro-pneumatic motor in operation provides a substantially constant force regardless of the speed of the ram of the press or other machine by which it is operated. In this respect, it differs in operation from the hydro-pneumatic motor 10, wherein the force exerted, such as a holddown force upon a workpiece, varies with the speed of the ram, and requires changes of the size of the central valve orifice in the valve disc 82 in order to prevent the holddown force from increasing in an undesired manner with an increase in the speed of the ram, or when used with a press having a different ram speed. The compound flow control valve unit 152 of the modified hydro-pneumatic motor 150 provides this additional feature of keeping the holddown force of the motor 158 substantially constant, notwithstanding its adaptation to presses of different ram speeds. In other respects, the modified motor 150 operates similarly to the motor 10, hence only a brief description of the operation is required.

During the forward or working stroke of the main ram or hydraulic plunger 118, the hydraulic piston 153 will remain stationary until it is caused to exert a sufficient pressure on the hydraulic fluid entrapped in the chamber 44 to overcome the force of the spring 176 and move the hollow valve member 172 off its seat 162. This action permits hydraulic fluid to flow from the chamber 44 to the intermediate chamber 42 by way of the passageways 74 and 178. Thus, the excessive pressure is dispersed by this dumping of the hydraulic fluid, so that the holddown pressure remains constant. The faster the descent of the ram or platen 118 occurs, the quicker the dumping of the hydraulic fluid takes place, because the relief valve member 172 moves off its seat 162 sooner with a fast-moving ram than with a slow-moving ram.

After the working stroke has been completed, the upward motion of the ram 118 upon its retraction or return stroke permits consequent upward movement of the hydraulic plunger 153, whereupon the hydraulic fluid in the intermediate chamber 42 moves the valve head 156 downward off the valve seat 50. This action then permits flow of hydraulic fluid to take place around the edge of the valve head 156 from the chamber 42 through the passageways 60, 62 and 72 into the chamber 44, thereby emptying the intermediate chamber 42 and preparing the motor 150 for its next holddown or working stroke. Meanwhile, the spring 176 has forced the relief valve member 172 downward against its seat 162, closing off the flow of hydraulic fluid through the central passageway 74. Adequate return of fluid, however, is afforded by providing a sufiicient number of the marginal passageways 60, 62, 72, not withstanding the blocking oflf of the central passageway 74 by the relief valve member 172 during the return or retraction stroke.

The words upward and downward are of course employed herein in a purely relative sense according to the assumption that the hydro-pneumatic motors 10 are mounted in a vertical position. It will be evident from FIGURES 1, 2 and 6, however, that the hydraulic motors 10 or 150 can be mounted in horizontal positions or even in oblique positions according to the particular installation, in which case the corresponding motions of the plunger 24, piston 38 and the various other moving parts would be described as to the right or to the left, as the case might be.

What I claim is:

1. A reciprocable hydro-pneumatic motor, comprising a main cylinder having a cylinder bore therein forming a main hydraulic fluid chamber, a main piston having a main piston head reciprocable in said cylinder bore and a hollow piston rod extending exteiiorly thereof, said main piston head having a main hydraulic fluid passageway extending therethrough from said cylinder bore, said hollow piston rod having a longitudinal bore communieating with said main piston head passageway, and an auxiliary piston reciprocably mounted in said piston rod bore, said auxiliary piston subdividing said piston rod bore into an intermediate hydraulic fluid chamber on the side thereof facing said main piston head and a pneumatic fluid chamber on the opposite side thereof, said main piston head having an additional hydraulic fluid pass-ageway therethrough, unidirectional valve means disposed adjacent said main piston head in controlling relationship to the flow of hydraulic fluid through said additional hydraulic fluid passageway between said main hydraulic fluid chamber and said intermediate hydraulic fluid chamber, said valve means having an orifice of restricted diameter communicating with said main hydraulic fluid passageway and effecting retardation of hydraulic fluid flow therethrough, said valve means also including a valve seat at one end of said piston rod bore and a reciprocable valve member mounted adjacent said piston head and movable alternately into and out of closing relationship with said valve seat, said valve member having a passageway therethrough communicating constantly with said main hydraulic fluid passageway.

2. A reciprocable hydro-pneumatic motor, according to claim 1, wherein said passageway is of restricted diameter effecting retardation of hydraulic fluid flow therethrough.

3. A reciprocable hydro-pneumatic motor, comprising a main cylinder having a cylinder bore therein forming a main hydraulic fluid chamber, a main piston having a main piston head reciprocable in said cylinder bore and a hollow piston rod extending exteriorly thereof, said main piston head having a main hydraulic fluid passageway extending therethrough from said cylinder bore, said hollow piston rod having a longitudinal bore communicating with said main piston head passageway, and an auxiliary piston reciprocably mounted in said piston rod bore, said auxiliary piston subdividing said piston rod bore into an intermediate hydraulic fluid chamber on the side thereof facing said main piston head and a pneumatic fluid chamber on the opposite side thereof, said main hydraulic fluid passageway being disposed in the central portion of said main piston head and said main piston head having additional hydraulic fluid passageways disposed near the periphery of said main piston head in circumferentiallyspaced relationship, and a reciprocable valve member dis posed adjacent said main piston head in controlling relationship to the flow of hydraulic fluid through said additional fluid passageway between said main hydraulic fluid chamber and said intermediate hydraulic fluid chamber.

4. A reciprocable hydro-pneumatic motor, according to claim 3, wherein said valve member has an orifice therethrough communicating constantly with said main hydraulic fluid passageway.

5. A reciprocable hydro-pneumatic motor, comprising a main cylinder having a cylinder bore therein forming a main hydraulic fluid chamber, a main piston having a main piston head reciprocable in said cylinder bore and a hollow piston rod extending exteriorly thereof, said main piston head having a main hydraulic fluid passageway extending therethrough from said cylinder bore, said hollow piston rod having a longitudinal bore communicating with said main piston head passageway, and an auxiliary piston reciprocably mounted in said piston rod bore, said auxiliary piston subdividing said piston rod bore into an intermediate hydraulic fluid chamber on the side thereof facing said main piston head and a pneumatic fluid chamber on the opposite side thereof, said main piston head having an additional hydraulic fluid passageway therethrough, unidirectional valve means disposed adjacent said main piston head in controlling relationship to the flow of hydraulic fluid through said additional hydraulic passageway between said main hydraulic fluid chamber and said intermediate hydraulic fluid chamber, said valve means including a valve seat at one end of said piston rod bore and a reciprocable valve member mounted adjacent said main piston head and movable alternately into and out of closing relationship with said valve seat, said valve member having a passageway therethrough communicating with said main hydraulic fluid passageway, said valve member having an auxiliary valve member disposed in fluid-flow-controlling relationship with said main hydraulic fluid passageway.

6. A reciprocable hydro-pneumatic motor, according to claim 5, wherein yielding means engages and urges said auxiliary valve member into closing relationship with said main hydraulic fluid passageway.

7. A reciprocable hydro-pneumatic motor, according to claim 6, wherein said yielding means includes a spring within said valve member engaging said auxiliary valve member.

References Cited in the file of this patent UNITED STATES PATENTS 2,679,827 Perdue June 1, 1954 

